1. Field of the Invention
The present invention relates to a heat radiation device for memory modules which radiates heat that is generated from memory elements of each of the modules to cool the memory elements, in cases where a plurality of semiconductor memory modules, wherein a plurality of memory elements are installed on a memory substrate (hereinafter sometimes abbreviated to “module”), are placed in parallel on a mother board or the like to form a module group. The above-mentioned semiconductor memory modules are shown as an example, by DIMM (Dual Inline Memory module) wherein a plurality of SDRAM (Synchronous Dynamic Access Memory) are arranged on a memory substrate.
2. Description of the Related Art
An example of a module group is shown in FIG. 1. Module group 2 shown in FIG. 1 consists of three modules 2a to 2c. Each of modules 2a to 2c has memory substrate 3 and a plurality of (generally 16 numbers) memory elements 4 that are arranged along the longitudinal direction of substrate 3 on both front and rear face sides thereof. Memory substrate 3 for each of modules 2a to 2c is inserted into connector 5 placed at a constant spacing.
Heat generated from memory elements 4 installed on each of modules 2a to 2c is radiated through heat radiation and convection from the surfaces of memory elements 4, and this heat is conducted to mother board 1 via memory substrate 3 and connector 5, and is radiated from the surfaces of mother board 1 as well. In FIG. 1, heat radiation from the surfaces of memory elements 4, convection therefrom and heat radiation through mother board 1 are schematically shown by arrows X, Y and Z, respectively. Japanese laid-open patent publication No. 94399/1986 (Showa 61) discloses a circuit module which enhances the heat radiation effect by extending the peripheries of a circuit chip or circuit board each corresponding to memory substrate 3 shown in FIG. 1, up to the external portion of that case that accommodates the above-mentioned chip or board.
Moreover in the case of RIMM (Rambus In-line memory Module) wherein a plurality of memory elements that are installed on memory substrates function one by one, the load and heat generation per each memory element increase as compared with other memory modules wherein a plurality of memory elements function simultaneously. Thus as shown in FIG. 2, heat radiation plates 6 which radiate heat generated from memory elements 4 in the longitudinal direction of memory substrate 3 are installed on each of modules 2a to 2c. Heat radiation plates 6 are arranged so as to encompass memory elements 4 on both front and rear face side of memory substrate 3 for each of modules 2a to 2c, and are in contact with opposing memory elements 4. Accordingly, heat generated from a memory element which was installed on memory substrate is dispersed in longitudinal direction of said memory substrate via heat radiation plate 6 with which the memory element comes in contact, and is radiated from the surface of the heat radiation plate 6.
It is difficult to maintain module temperature at a stipulated value or lower by heat radiation realized by the structure as shown in FIG. 1. In particular, with regard to central module 2b among the three modules 2a to 2c shown in FIG. 1, the convectional heat radiation effect is lowered by barriers due to modules 2a and 2c both of which are on the outside of module 2b. Further, since module 2b receives heat from memory elements 4 installed on modules 2a and 2c both on the outside of module 2b, its temperature tends to be increased as compared with modules 2a, 2c. 
In addition, the structure as shown in FIG. 2 may or may not uniformize the temperature difference among modules 2a to 2c, but the temperature difference among a plurality of adjacent modules is not uniformized. In particular, the temperature raising tendency of central module 2b among the three modules 2a to 2c is the same as that in the structure shown in FIG. 1. In fact, three modules 2a to 2c shown in FIG. 2 were made to function simultaneously, and the temperatures thereof were measured. As a result, the highest temperature of central module 2b was 67.2° C., while that of modules 2a, 2c, both on the outside was, 61.6° C., thereby causing a temperature difference of 5.0° C. or higher.
As mentioned above, in the case where a plurality of modules are placed in parallel on a mother board or the like, much difference in temperature is caused among each of the modules, thus bringing about scattering of characteristic parameters (setup time, hold time and the like) of the memory elements that are installed on each of the modules. The scattering of characteristic parameters of the memory elements induces system malfunction. Further, if working frequency of memory elements further increases hereafter, there is also a danger of thermal breakage of memory elements.